Lathe-type machines including a headstock and a relatively wingable tool carriage, have been provided in the past with various attachments for advancing or retacting a cutting tool relative to the face of the rotating workpiece in order to produce aspherical surfaces. Often these attachments include cams or patterns, one for each particular curved aspherical surface to be produced on the workpiece. Other attachments have been provided which do not use a plurality of cams for the different curvatures but accomplish the necessary advancement and retraction of the tool in various ways.
The present invention provides a lathe-type machine in which the advancement and retraction of the cutting tool relative to the face of the workpiece, to obtain aspherical surfaces, is accomplished by a very simple and effective eccentric control unit which cooperates with the tool carriage to move it back-and-forth relative to the headstock during the swinging movement of the tool carriage about its pivot. The eccentric unit is such that it can be set for selected infinite variations of curves to be reproduced on the workpiece and the setting can be accomplished accurately and quickly by un-skilled persons.
The present invention will be described with reference to a lathe which is especially useful in cutting contact lenses of special characteristics or curvatures. However, the machine is useful in cutting, or otherwise generating, on various workpieces, surfaces of special characteristics.
Below are set forth examples of various types of cuts of contact lenses which the lathe of this invention is capable of producing in a single operation:
1. Cuts concave and convex curves either spherical or aspherical. PA1 2. Cuts concave and convex curves that are spherical in the center with gradual flattening towards the periphery (a semi-spherical cut). PA1 3. Cuts concave curves with a continuous change of radius from the center to the periphery (aspherical type). PA1 4. Cuts convex curves with a continuous change of radius from the center to the periphery (aspherical type). PA1 5. Cuts convex curves that are spherical in the center with a rapid change of radius at a determined point, producing a convex curve cut known as "lenticular cut" in the lens art and of a determined positive or negative value.
The lathe described herein provides extreme agility in its operation, maintaining a high degree of precision despite continued use, and achieving an easy reproduction of complex lenses with extraordinary simplicity.